In many industrial applications a variable volume positive displacement pump is utilized to provide hydraulic energy to drive mechanical devices, such as a hydraulic motor. Variable volume positive displacement pumps are driven by prime movers, such as engines or motors. In many applications it is desirable that the output of a variable volume positive displacement pump be maintained as near as possible to the horsepower delivering capabilities of the prime mover or to some lower pre-selected horsepower. That is, if the pressure of fluid at the discharge of the pump increases, the volume must be decreased otherwise the horsepower input requirement to the pump must increase. Correspondingly, if the pressure decreases, the volume must be increased otherwise the horsepower input to the pump will diminish. In some applications it is desirable that the maximum pressure of the pump be obtained without exceeding the maximum horsepower capability of the prime mover.
In order to vary the output of a positive displacement hydraulic pump it is necessary to mechanically vary some control of the pump, such as a control arm extending from the pump. The present invention is directed toward a control device for controlling a hydraulic pump in such a way as to maintain substantially constant hydraulic horsepower output.
It is therefore an object of this invention to provide a control device for converting a hydraulic pressure signal to a mechanical motion, the mechanical displacement being directly proportional to the value of the hydraulic signal.
More particularly, an object of this invention is to provide a hydraulic system for producing a constant horsepower input to a hydraulic fluid utilizing apparatus, such as a hydraulic motor, the system including a prime mover connected to a variable volume positive displacement pump and a controller for sensing the pressure at the output of the pump and for controlling the pump to increase the volume when the pressure drops and to decrease the volume as the pressure rises in a linear way so as to maintain the horsepower output, and therefore the horsepower input requirements of the pump, substantially constant.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.